In the current version of Netsuite, the Audience settings of a category are not inherited by the Items published in it which makes them searchable in the Default Global Search from Setup > Site Builder > Set Up Web Site > Search tab.
To keep the Audience settings by using the Price level as a workaround here are the steps:
1. Set a Price level to the customer record that has access to the Audience restricted category:
a. Edit the customer record.
b. Navigate to the Financial Tab.
c. Set a Price level for the customer which is different from the Global settings at Setup > Site Builder > Set Up Web Site > Setup tab. For example, use an Alternative price level for the customer if Online Price is set globally.
d. Click Save.
2. Add a price level to the item record published to the audience restricted category.
a. Edit the item record.
b. Navigate to the Pricing tab.
c. Remove the amount at the Global Online Price level from above (from the example leave the Online Price level field blank).
Note:This will make the item hidden to visitors that are not logged in the site and will not appear in keyword searches.
d. Enter an amount to the price level field set with the customer record from step 1.
e. Click Save.